I'm just getting started with contributing. My CPU is weak, but I have 3 980ti & would like to only take on Blender GPU tasks. How do I set this preference? I am on ubuntu 16.04 and installed with boinc with APT. I can't find a config file to edit.

Take a look into your account, search for the "BURP settings", and edit them to only "use NVidia GPU". That should do the trick.
However, this requires that there is work and sessions for the GPU available, and currently this is not the case. In fact, GPU units were very rare the last months. Aadditionally, looking at the apps page I assume the GPU apps were removed a while ago, maybe because it's still in development. Don't know when it will be back.
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The CPU apps are multi-threaded, so that's a plus--we can always use your help. Also, spread the word! We need both crunchers, and animators to submit new sessions to be rendered.
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